Local Perception of Drought Impacts in a Changing Climate: The Mega-Drought in Central Chile

Sustainability

10.3390/su9112053

Droughts are a recurrent and complex natural hazard whose frequency and magnitude are expected to increase with climate change. Despite the advances in responding and adapting to droughts (with the development of new policies, for example), droughts continue to cause serious impacts and suffering. Developing well-targeted public policies requires further research on adaptation. Specifically, understanding the public perception of drought can help to identify drivers of and barriers to adaptation and options. This research seeks to understand the public perception of drought in central Chile in order to inform adaptation-related policies and decision-making processes. This study focused on the Mega-drought, which was a protracted dry spell afflicting central Chile since 2010.

On January 4, 2014, during the summer period in South America, an intense forest and dry pasture wildfire occurred nearby the city of Santiago de Chile. On that day the biomass-burning plume was transported by low-intensity winds towards the metropolitan area of Santiago and impacted the concentration of pollutants in this region. In this study, the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem) is implemented to investigate the biomass-burning plume associated with these wildfires nearby Santiago, which impacted the ground-level ozone concentration and exacerbated Santiago's air quality. Meteorological variables simulated by WRF/Chem are compared against surface and radiosonde observations, and the results show that the model reproduces fairly well the observed wind speed, wind direction air temperature and relative humidity for the case studied. Based on an analysis of the transport of an inert tracer released over the locations, and at the time the wildfires were captured by the satellite-borne Moderate Resolution Imaging Spectroradiometer (MODIS), the model reproduced reasonably well the transport of biomass burning plume towards the city of Santiago de Chile within a time delay of two hours as observed in ceilometer data. A six day air quality simulation was performed: the first three days were used to validate the anthropogenic and biogenic emissions, and the last three days (during and after the wildfire event) to analyze the performance of WRF/Chem plume-rise model within FINNv1 fire emission estimations. The model presented a satisfactory performance on the first days of the simulation when contrasted against data from the well-established air quality network over the city of Santiago de Chile. These days represent the urban air quality base case for Santiago de Chile unimpacted by fire emissions. However, for the last three simulation days, which were impacted by the fire emissions, the statistical indices showed a decrease in the model performance. While the model showed a satisfactory evidence that wildfires plumes that originated in the vicinity of Santiago de Chile were transported towards the urban area and impacted the air quality, the model still underpredicted some pollutants substantially, likely due to misrepresentation of fire emission sources during those days. Potential uncertainties may include to the land use/land cover classifications and its characteristics, such as type and density of vegetation assigned to the region, where the fire spots are detected. The variability of the ecosystem type during the fire event might also play a role.

The 2010-2015 mega drought in Central Chile: Impacts on regional hydroclimate and vegetation

Hydrology and Earth System Sciences Discussions

10.5194/hess-2017-191

Since 2010 an uninterrupted sequence of dry years, with annual rainfall deficits ranging from 25 to 45 %, has prevailed in Central Chile (western South America, 30–38° S). Although intense 1- or 2-year droughts are recurrent in this Mediterranean-like region, the ongoing event stands out because of its longevity and large spatial extent. The extraordinary character of the so-called Central Chile Mega Drought (MD) was established against century long historical records and a millennial tree-ring reconstruction of regional precipitation. The largest MD-averaged rainfall relative anomalies occurred in the northern, semi-arid sector of central Chile but the event was unprecedented to the south of 35° S. ENSO neutral conditions have prevailed since 2011 (but for the strong El Niño 2015) contrasting with La Niña conditions that often accompanied past droughts. The precipitation deficit diminished the Andean snowpack and resulted in amplified declines (up to 90 %) of river flow, reservoir volumes and groundwater levels along central Chile and westernmost Argentina. In some semiarid basins we also found a conspicuous decrease in the runoff-to-rainfall coefficient. A substantial decrease in vegetation productivity occurred in the shrubland-dominated, northern sector, but a mix of greening and browning patches occurred farther south where irrigated croplands and exotic forest plantations dominate. The ongoing warming in central Chile, making the MD one of the warmest 6-year period on record, may have also contributed to such complex vegetation changes by increasing potential evapotranspiration. The understanding of the nature and biophysical impacts of the MD contributes to preparedness efforts to face a dry, warm future regional climate scenario.

https://www.hydrol-earth-syst-sci-discuss.net/hess-2017-191/

1-37

Thomson Reuters ISI

Agua y Extremos

2017

González, S., Garreaud, R.

Spatial variability of near-surface temperature over the coastal mountains in southern Chile (38°S)

The spatial distribution of the near-surface air temperature over a coastal mountain range in southern Chile [Nahuelbuta Mountains (NM), 38°S, maximum height 1300-m ASL] is investigated using in situ measurements, satellite-derived land-surface temperature, and simulations during the austral winter of 2011. Based on a few selected but representative cases, we found that under rainy conditions—either at day or night—temperature decreases with height close to the moist adiabatic lapse rate (~6.5 °C/km). Likewise, the temperature tends to follow the dry adiabat (~9.8 °C/km) during daytime under dry- and clear-skies conditions. During clear-skies nights, the temperature also decreases with height over the southeastern side of NM, but it often increases (at about 8 °C/km) over the northwestern side of the mountains. This temperature inversion extends up to about 700-m ASL leading to an average temperature contrast of about 7 °C between the northwestern and southeastern sides of Nahuelbuta by the end of dry nights. These dawns also feature substantial temperature differences (>10 °C) among closely located stations at a same altitude. High-resolution numerical simulations suggest that upstream blocking of the prevailing SE flow, hydrostatic mountain waves, and strong downslope winds is responsible for such distinctive nocturnal temperature distribution.

Research on Climate Change Policies and Rural Development in Latin America: Scope and Gaps

Sustainability

10.3390/su9101831

Research on climate change policies can contribute to policy development by building an understanding of the barriers faced in policy processes, and by providing knowledge needed throughout policy cycles. This paper explores the thematic coverage of research on climate change policies related to rural areas, rural development, and natural resource management in Latin America. A three-tier framework is proposed to analyse the selected literature. The results show that research studies have focussed on the mitigation of greenhouse gas emissions from forests, and adaptations to climate change in agriculture. There is little policy research on other vulnerable sectors (e.g., water and health) and emitting sectors (e.g., energy and industry) in the context of rural development. Our analysis highlights the various research gaps that deserve increased scientific attention, including: cross-sector approaches, multi-level governance, and the stages of policy adoption, implementation and evaluation. In addition, the selected literature has a limited contribution to theoretical discussions in policy sciences.

The Chilean Coastal Orographic Precipitation Experiment (CCOPE) was conducted during the austral winter of 2015 (May-August) in the Nahuelbuta Mountains (peak elevation 1.3 km MSL) of southern Chile (38°S). CCOPE used soundings, two profiling Micro Rain Radars, a Parsivel disdrometer, and a rain gauge network to characterize warm and ice-initiated rain regimes and explore their consequences for orographic precipitation. Thirty-three percent of foothill rainfall fell during warm rain periods, while 50% of rainfall fell during ice-initiated periods. Warm rain drop size distributions were characterized by many more and relatively smaller drops than ice-initiated drop size distributions. Both the portion and properties of warm and ice-initiated rainfall compare favorably with observations of coastal mountain rainfall at a similar latitude in California. Orographic enhancement is consistently strong for rain of both types, suggesting that seeding from ice aloft is not a requisite for large orographic enhancement. While the data suggest that orographic enhancement may be greater during warm rain regimes, the difference in orographic enhancement between regimes is not significant. Sounding launches indicate that differences in orographic enhancement are not easily explainable by differences in low-level moisture flux or nondimensional mountain height between the regimes.

Tree-ring anatomical anomalies have received little attention in southern South American trees, however they can contain valuable intra-annual environmental information. This study addressed for the first time the three most frequent tree- ring anomalies recorded in the northern and oldest known Austrocedrus chilensis forest in central Chile (32-35°S). Three anatomic anomalies described were: partially absent rings, intra-annual bands and frost rings. Partially absent rings resulted from cambial inactivity during a complete growing period and require dendrochronological tools to be detected. Intra- annual bands are consequence of the abundance-shortage of environmental resources during the growing season and can be detected by examining the undefined late-wood boundaries. Frost rings, are caused by extreme low temperatures and are characterized by collapsed cells in the tree-ring growth. Results indicate that the northern most population exhibited the highest rate of absent rings, while the occurrence of intra-annual bands seems to be rather minor in the study area. Finally, frost rings are registered mainly in the younger trees in all three studied sites. These results suggest the potential for future spatio-temporal studies that examine the frequency of these anatomical anomalies in A. chilensis chronologies along its wide geographical distribution. This will complement the current environmental information recorded by its growth rates.

Climate change and resilience of deciduous Nothofagus forests in central-east Chilean Patagonia over the last 3200 years: RESILIENCE OF DECIDUOUS NOTHOFAGUS FORESTS IN PATAGONIA

Journal of Quaternary Science

10.1002/jqs.2948

We examine the response of Nothofagus forests to climate change and disturbance regimes over the last 3200 years near Coyhaique (45°S), central–east Chilean Patagonia, using fine‐resolution pollen and charcoal records from lake sediment cores. Closed‐canopy deciduous Nothofagus forests have dominated the region with little variation until the arrival of Chilean–European settlers, suggesting a predominance of cool‐temperate and wet conditions. Within this state we identify centennial‐scale episodes of forest fragmentation, increase in littoral macrophytes and volcanic/paleofire disturbance between 2700 and 3000 cal a BP, 2200 and 2500 cal a BP and over the last ∼250 years, which we interpret as intervals with negative hydrologic balance. Natural variability caused little impact on the physiognomy and composition of the vegetation in pre‐European time, in contrast to the accelerated shift that started during the late 19th century associated with deforestation, homogenization and synchronization of ecosystem changes at the landscape level, and spread of exotic plant species brought by Chilean and European settlers during a warm/dry interval. The resilience of deciduous Nothofagus forests to natural disturbance regimes and climate change was exceeded by large‐scale human disturbance since the late 19th century by fire, timber exploitation and livestock grazing. These disturbances caused an ecosystem shift towards artificial meadows and scrublands with frequent high‐magnitude fires.

Temporal and spatial evaluation of satellite rainfall estimates over different regions in Latin-America

Atmospheric Research

10.1016/j.atmosres.2018.05.011

In developing countries, an accurate representation of the spatio-temporal variability of rainfall is currently severely limited, therefore, satellite-based rainfall estimates (SREs) are promising alternatives. In this work, six state-of-the-art SREs (TRMM 3B42v7, TRMM 3B42RT, CHIRPSv2, CMORPHv1, PERSIANN-CDR, and MSWEPv2) are evaluated over three different basins in Latin-America, using a point-to-pixel comparison at daily, monthly, and seasonal timescales. Three continuous (root mean squared error, modified Kling-Gupta efficiency, and percent bias) and three categorical (probability of detection, false alarm ratio, and frequency bias) indices are used to evaluate the performance of the different SREs, and to assess if the upscaling procedure used, in CHIRPSv2 and MSWEPv2, to enable a consistent point-to-pixel comparison affects the evaluation of the SREs performance at different time scales.

Our results show that for Paraiba do Sul in Brazil, MSWEPv2 presented the best performance at daily and monthly time scales, while CHIRPSv2 performed the best at these timescales over the Magdalena River Basin in Colombia. In the Imperial River Basin in Chile, MSWEPv2 and CHIRPSv2 performed the best at daily and monthly time scales, respectively. When the basins were evaluated at seasonal scale, CMORPHv1 performed the best for DJF and SON, TRMM 3B42v7 for MAM, and PERSIANN-CDR for JJA over Imperial Basin. MSWEPv2 performed the best over Paraiba do Sul Basin for all seasons and CHIRPSv2 showed the best performance over Magdalena Basin. The Modified Kling-Gupta efficiency (KGE′) proved to be a useful evaluation index because it decomposes the performance of the SREs into linear correlation, bias, and variability parameters, while the Root Mean Squared Error (RMSE) is not recommended for evaluating SREs performance because it gives more weight to high rainfall events and its results are not comparable between areas with different precipitation regimes.

On the other hand, CHIRPSv2 and MSWEPv2 presented different performance, for some study areas and time scales, when evaluated with their original spatial resolution (0.05° and 0.1, respectively) with respect to the evaluation resulting after applying the spatial upscaling (to a unified 0.25), showing that the upscaling procedure might impact the SRE performance. We finally conclude that a site-specific validation is needed before using any SRE, and we recommend to evaluate the SRE performance before and after applying any upscaling procedure in order to select the SRE that best represents the spatio-temporal precipitation patterns of a site.

http://linkinghub.elsevier.com/retrieve/pii/S0169809517313029

Thomson Reuters ISI

Agua y Extremos

2018

Barria, P., Peel, M. C., Walsh, K. J. E., Muñoz, A.

The first 300-year streamflow reconstruction
of a high-elevation river in Chile using tree rings

International Journal of Climatology

10.1002/joc.5186

In central Chile, increasing demand for water and decreasing runoff volumes due to drier conditions have placed catchments in this zone under water stress. However, scarcity of observed data records increases the difficulty of planning future water supply. Instrumental records suggest a reduction in streamflow over the last 56 years. However, this change is not statistically significant and the lack of meteorological stations with long records in this mountainous region hampers a deeper analysis, motivating the use of tree rings to analyse whether these changes are part of a long-term trend. This work represents the first high-elevation runoff reconstruction in Chile using 300 years of tree ring chronologies of Araucaria araucana and Astroceudrus chilensis. The upper part of Biobío river melting season runoff (October–March) and pluvial season runoff (April–September) was reconstructed and analysed to investigate the influence of large-scale climatic drivers on runoff generation, current drought trends and to improve the understanding of climate variability in this region. We obtained positive correlations between the 20-year moving average of reconstructed pluvial season runoff and reconstructed Pacific Decadal Oscillation (PDO), which is indicative of multi-decadal variability. We also found a negative correlation between the 11-year moving average of reconstructed melting season runoff and the PDO and positive correlations with the Southern Annular Mode (SAM). Important differences in the runoff variability of the upper and the lower part of the catchment were identified which are in part led by the influence of the large-scale climatic features that drive runoff generation in both regions. We found that the changes observed in the instrumental records are part of multi-decadal cycles led by the PDO and SAM for pluvial season runoff and melting season runoff, respectively.

http://doi.wiley.com/10.1002/joc.5186

436-451

vol.38 is.1

Thomson Reuters ISI

Agua y Extremos; Zonas Costeras; Transversal

2018

Bozkurt, D., Rondanelli, R., Marín, J. C., Garreaud, R.

Foehn Event Triggered by an Atmospheric River Underlies Record-Setting Temperature Along Continental Antarctica

Journal of Geophysical Research: Atmospheres

10.1002/2017JD027796

A record‐setting temperature of 17.5°C occurred on 24 March 2015 at the Esperanza station located near the northern tip of the Antarctic Peninsula (AP). We studied the event using surface station data, satellite imagery, reanalysis data, and numerical simulations. The Moderate Resolution Imaging Spectroradiometer Antarctic Ice Shelf Image Archive provides clear evidence for disintegration and advection of sea ice, as well as the formation of melt ponds on the ice sheet surface at the base of the AP mountain range. A deep low‐pressure center over the Amundsen‐Bellingshausen Sea and a blocking ridge over the southeast Pacific provided favorable conditions for the development of an atmospheric river with a northwest‐southeast orientation, directing warm and moist air toward the AP, and triggering a widespread foehn episode. A control simulation using a regional climate model shows the existence of local topographically induced warming along the northern tip of the AP (∼60% of the full temperature signal) and the central part of the eastern AP (>90% of the full temperature signal) with respect to a simulation without topography. These modeling results suggest that more than half of the warming experienced at Esperanza can be attributed to the foehn effect (a local process), rather than to the large‐scale advection of warm air from the midlatitudes. Nevertheless, the local foehn effect also has a large‐scale advection component, since the atmospheric river provides water vapor for orographic precipitation enhancement and latent heat release, which makes it difficult to completely disentangle the role of local versus large‐scale processes in explaining the extreme event.

Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.

Dendrohydrology and water resources management in south-central Chile: lessons from the Río Imperial streamflow reconstruction

Hydrology and Earth System Sciences

10.5194/hess-22-2921-2018

Streamflow in south-central Chile (SCC, ∼ 37–42° S) is vital for agriculture, forestry production, hydroelectricity, and human consumption. Recent drought episodes have generated hydrological deficits with damaging effects on these activities. This region is projected to undergo major reductions in water availability, concomitant with projected increases in water demand. However, the lack of long-term records hampers the development of accurate estimations of natural variability and trends. In order to provide more information on long-term streamflow variability and trends in SCC, here we report findings of an analysis of instrumental records and a tree-ring reconstruction of the summer streamflow of the Río Imperial ( ∼ 37° 40′ S–38° 50′ S). This is the first reconstruction in Chile targeted at this season. Results from the instrumental streamflow record ( ∼ 1940 onwards) indicated that the hydrological regime is fundamentally pluvial with a small snowmelt contribution during spring, and evidenced a decreasing trend, both for the summer and the full annual record. The reconstruction showed that streamflow below the average characterized the post-1980 period, with more frequent, but not more intense, drought episodes. We additionally found that the recent positive phase of the Southern Annular Mode has significantly influenced streamflow. These findings agree with previous studies, suggesting a robust regional signal and a shift to a new hydrological scenario. In this paper, we also discuss implications of these results for water managers and stakeholders; we provide rationale and examples that support the need for the incorporation of tree-ring reconstructions into water resources management.

The far eastern tropical Pacific experienced a rapid, marked warming in early 2017, causing torrential rains along the west coast of South America with a significant societal toll in Peru and Ecuador. This strong coastal El Niño was largely unpredicted, even a few weeks before its onset, and it developed differently from either central or eastern events. Here we provide an overview of the event, its impacts and concomitant atmospheric circulation. It is proposed that a remotely forced, sustained weakening of the free tropospheric westerly flow impinging the subtropical Andes leads to a relaxation of the southeasterly (SE) trades off the coast, which in turn may have warmed the eastern Pacific throughout the weakening of upwelling in a near-coastal band and the lessening of the evaporative cooling farther offshore.

http://doi.wiley.com/10.1002/joc.5426

Thomson Reuters ISI

Agua y Extremos

2018

Garreaud, R. D.

Record-breaking climate anomalies lead to severe drought and environmental disruption in western Patagonia in 2016

Traditionally a temperate and hyper-humid region, western Patagonia experienced its most severe drought during the summer and fall of 2016. Along with precipitation deficits larger than 50% there was a similar reduction in river discharge into coastal waters, a decline in vegetation productivity, excessive solar radiation at the surface, and frequent upwelling-favorable wind events offshore. The combination of these regional-scale anomalies seems to have set the stage for environmental disturbances that, although not new in western Patagonia, occurred with unprecedented magnitude, including severe urban air pollution episodes, large forest fires, and the worst ever recorded harmful algae bloom (HAB). The local climate anomalies were in turn related to the concomitant strong El Niño (through atmospheric teleconnections) and, to a lesser extent, anthropogenic climate change mediated by the positive polarity of the Southern Annular Mode (SAM) and internal variability, as both modes weakened the westerlies. Dryer than present conditions are consistently projected for northern Patagonia during the 21st century as a consequence of anthropogenic increases in radiative forcing; superposition of El Niño events in this altered climate may result in a higher frequency of extreme droughts and environmental disruptions like those observed in 2016.

A harmful algal bloom (HAB) of the raphidophyta alga Pseudochattonella cf. verruculosa during the 2016 austral summer (February-March) killed nearly 12% of the Chilean salmon production, causing the worst mass mortality of fish and shellfish ever recorded in the coastal waters of western Patagonia. The HAB coincided with a strong El Ninõ event and the positive phase of the Southern Annular Mode that altered the atmospheric circulation in southern South America and the adjacent Pacific Ocean. This led to very dry conditions and higher than normal solar radiation reaching the surface. Using time series of atmospheric, hydrologic and oceanographic data we show here that an increase in surface water temperature and reduced freshwater input resulted in a weakening of the vertical stratification in the fjords and sounds of this region. This allowed the advection of more saline and nutrient-rich waters, ultimately resulting in an active harmful algal bloom in coastal southern Chile.

http://www.nature.com/articles/s41598-018-19461-4

vol.8 is.1

Thomson Reuters ISI

Agua y Extremos, Gobernanza e Interfaz entre Ciencia y Política

2018

Lillo-Ortega, G., Aldunce, P., Adler, C., Vidal, M., Rojas, M.

On the evaluation of adaptation practices: a transdisciplinary exploration of drought measures in Chile

Sustainability Science

10.1007/s11625-018-0619-5

A severe drought has affected central Chile since 2009. Various adaptation responses have been developed, and a participatory process is required to learn from them. To enable this, a transdisciplinary approach was adopted to achieve two objectives: first, to test an approach for assessing the effectiveness of existing measures to respond to drought, specifically to distil strengths and weaknesses of implementation, and developing recommendations; second, to reflect on results from a pilot project conducted to ascertain its potential for scalability in terms of processes employed. The research was organized per the three types of knowledge needed to address complex problems through transdisciplinarity: systems, target and transformation knowledge. Using the recent drought as a boundary object, we conducted the pilot in two locations in Chile where we carried out literature reviews, interviews and focus group discussions were carried out. We identified adaptation measures at national and local scale, a set of which were evaluated applying the Index for the Usefulness of Adaptation Practices (IUPA). Results indicate that through IUPA, we could systematically account for the perceived effectiveness of applied measures. Strengths such as autonomy in the decision-making process emerged as key factors that could also be applied in other contexts, whereas weaknesses such as lack of integration with other policy domains, programs or projects were identified. To address weaknesses, key recommendations were proposed, which are congruent with context-specific expectations, capacities, experiences and knowledge, given that they were articulated by local actors. Results present empirical evidence on the important utility of transdisciplinary approaches in the evaluation of adaptation measures and can support the development of metrics related to adaptation process at the local scale.

http://link.springer.com/10.1007/s11625-018-0619-5

Thomson Reuters ISI

Agua y Extremos

2018

Lucas C., Puchi P., Profumo L., Ferreira A., Muñoz A.

Effect of climate on tree growth in the Pampa biome of Southeastern South America: First tree-ring chronologies from Uruguay

Dendrochronologia

10.1016/j.dendro.2018.10.004

Tree-ring research in the highland tropics and subtropics represents a major frontier for understanding climate-growth relationships. Nonetheless, there are many lowland regions – including the South American Pampa biome – with scarce tree ring data. We present the first two tree-ring chronologies for Scutia buxifolia in subtropical Southeastern South America (SESA), using 54 series from 29 trees in two sites in northern and southern Uruguay. We cross-dated annual rings and compared tree growth from 1950 to 2012 with regional climate variability, including rainfall, temperature and the Palmer Drought Severity Index – PDSI, the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Overall, ring width variability was highly responsive to climate signals linked to water availability. For example, tree growth was positively correlated with accumulated rainfall in the summer-fall prior to ring formation for both chronologies. Summer climate conditions were key for tree growth, as shown by a negative effect of hot summer temperatures and a positive correlation with PDSI in late austral summer. The El Niño phase in late spring/early summer favored an increase in rainfall and annual tree growth, while the La Niña phase was associated with less rainfall and reduced tree growth. Extratropical climate factors such as SAM had an equally relevant effect on tree growth, whereby the positive phase of SAM had a negative effect over radial growth. These findings demonstrate the potential for dendroclimatic research and climate reconstruction in a region with scarce tree-ring data. They also improve the understanding of how climate variability may affect woody growth in native forests – an extremely limited ecosystem in the Pampa biome.

https://linkinghub.elsevier.com/retrieve/pii/S1125786518300249

113-122

Vol.52

Thomson Reuters ISI

Agua y Extremos

2018

Moreno, P. I., Vilanova, I., Villa-Martínez, R. P., Francois, J. P.,

Modulation of Fire Regimes by Vegetation and Site Type in Southwestern Patagonia Since 13 ka

Frontiers in Ecology and Evolution

10.3389/fevo.2018.00034

The degree to which vegetation and site type have influenced fire regimes through the Holocene has not been investigated in detail in the temperate ecosystems of southern Patagonia. Here we present a first attempt using a paired-basin approach to study the evolution of fire regimes in sectors dominated by humid Nothofagus forests and the xeric Patagonian steppe in the Magallanes region of Chilean Patagonia (51°S). We analyzed sediment cores from two small lakes and a bog located within the same climate zone on opposite sides of the forest-steppe ecotone, ~28 km apart. The position of this biological boundary east of the Andes is controlled by the strength and position of the southern westerly winds, which constitute the sole source of precipitation throughout western Patagonia. Our results indicate that fires have occurred in the study region repeated times over the last ~13,000 years at bi- and tridecadal timescales. Sectors currently dominated by Patagonian steppe feature high frequency and low magnitude of local fires, and vice versa in humid forests. Climate-driven expansion of Nothofagus scrubland/woodland into steppe environments over the last ~4,200 years increased the magnitude and lowered the frequency of fire events, culminating with peak Nothofagus abundance, fire magnitude and frequency during the last millennium. We also detect divergences between lake-based vs. bog-based paleofire histories among paired sites located within the Patagonian steppe, ~12 km apart, which we attribute to local burning of the bog at times of lowered water table. This divergence suggests to us that bog-based vegetation and fire histories exacerbate a local, azonal, signal blurring extra-local or regional regimes, thus accounting for some discrepancies in the Quaternary paleovegetation/paleoclimate literature of southern Patagonia.

The Southern Westerly Winds (SWW) are the surface expression of geostrophic winds that encircle the southern mid-latitudes. In conjunction with the Southern Ocean, they establish a coupled system that not only controls climate in the southern third of the world, but is also closely connected to the position of the Intertropical Convergence Zone and CO2 degassing from the deep ocean. Paradoxically, little is known about their behavior since the last ice age and relationships with mid-latitude glacier history and tropical climate variability. Here we present a lake sediment record from Chilean Patagonia (51°S) that reveals fluctuations of the low-level SWW at mid-latitudes, including strong westerlies during the Antarctic Cold Reversal, anomalously low intensity during the early Holocene, which was unfavorable for glacier growth, and strong SWW since ∼7.5 ka. We detect nine positive Southern Annular Mode-like events at centennial timescale since ∼5.8 ka that alternate with cold/wet intervals favorable for glacier expansions (Neoglaciations) in southern Patagonia. The correspondence of key features of mid-latitude atmospheric circulation with shifts in tropical climate since ∼10 ka suggests that coherent climatic shifts in these regions have driven climate change in vast sectors of the Southern Hemisphere at centennial and millennial timescales.

Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.

Climate variability and forest fires in central and south-central Chile

Ecosphere

10.1002/ecs2.2171

This paper evaluates the relationship between fire occurrence (number and burned area) and
climate variability (precipitation and maximum temperatures) across central and south-central Chile
(32°–43° S) during recent decades (1976–2013). This region sustains the largest proportion of the Chilean
population, contains ecologically important remnants of endemic ecosystems, the largest extension of
forest exotic plantations, and concentrates most of the fire activity in the country. Fire activity in central
Chile was mainly associated with above-average precipitation during winter of the previous year and
with dry conditions during spring to summer. The later association was particularly strong in the southern,
wetter part of the study region. Maximum temperature had a positive significant relationship with
burned area across the study region, with stronger correlations toward the south. Fires in central Chile
were significantly related to El Nino~ –Southern Oscillation, through rainfall anomalies during the year
previous to the fire season. The Antarctic Oscillation during winter through summer was positively
related to fires across the study area due to drier/warmer conditions associated with the positive polarity
of this oscillation. Climate change projections for the region reveal an all-season decrease in precipitation
and increases in temperature, that may likely result in an increment of the occurrence and the area
affected by fires, as it has been observed during a multi-year drought afflicting central Chile since 2010.

http://doi.wiley.com/10.1002/ecs2.2171

e02171

vol.9 is.4

Thomson Reuters ISI

Agua y Extremos

2018

Valenzuela, R. A., Kingsmill, D. E.

Terrain-Trapped Airflows and Orographic Rainfall along the Coast of Northern California. Part II: Horizontal and Vertical Structures Observed by a Scanning Doppler Radar

Monthly Weather Review

10.1175/MWR-D-17-0227.1

This study documents the mean properties and variability of kinematic and precipitation structures associated with orographic precipitation along the coast of Northern California in the context of terrain-trapped airflows (TTAs). TTAs are defined as relatively narrow air masses that consistently flow in close proximity and approximately parallel to an orographic barrier. Seven land-falling winter storms are examined with observations from a scanning X-band Doppler radar deployed on the coast at Fort Ross, California. Additional information is provided by a 915-MHz wind-profiling radar, surface meteorology, a GPS receiver, and balloon soundings. The composite kinematic structure during TTA conditions exhibits a significant horizontal gradient of wind direction from the coast to approximately 50 km offshore and a low-level jet (LLJ) that surmounts a weaker airflow offshore corresponding to the TTA, with a zone of enhanced precipitation evident between ~5 and 25 km offshore and oriented nearly parallel to the coastline. Conversely, the composite kinematic structure during NO-TTA conditions exhibits a smaller offshore horizontal gradient of wind direction and precipitation structures are generally enhanced within ~15 km of the coastline. Interstorm variability analysis reveals significant variations in kinematic structures during both TTA and NO-TTA conditions, whereas significant variations in precipitation structures are only evident during TTA conditions. The interstorm analysis also illustrates more clearly how LLJ vertical structures evident during NO-TTA conditions exhibit ascent along the coast and over the coastal mountains, which is in contrast to TTA conditions where the ascent occurs offshore and over the TTA.

http://journals.ametsoc.org/doi/10.1175/MWR-D-17-0227.1

2381-2402

vol.146 is.8

Thomson Reuters ISI

Agua y Extremos

2018

Viale M., Valenzuela R., Garreaud R.D., Ralph F.M.

Impacts of Atmospheric Rivers on Precipitation in Southern South America

The 2010-2015 Megadrought and its influence on the fire regime in central and south-central Chile

Ecosphere

10.1002/ecs2.2300

Forest ﬁre activity has increased in recent years in central and south-central Chile. Drought conditions have been associated with the increase of large wildﬁres, area burned and longer ﬁre seasons. This study examines the inﬂuence of drought on ﬁre regimes and discusses landscape management opportunities to decrease ﬁre hazard. Speciﬁcally, we investigate the effect of the 2010–2015 Megadrought (MD) compared to 1990–2009 period on ﬁre activity (ﬁre-season length, number of ﬁres and burned area across months, ﬁre sizes, regions and vegetation cover types, simultaneity, and duration of ﬁres) in central and south-central Chile (32°–39° S), using contemporary ﬁre statistics derived from the Chilean Forest Service. For large ﬁre events (>200 ha) the average season length increased by 67 d (44%), comparing 2010–2015 to 1990–2009. Earlier and later ignition dates resulted in extended ﬁre seasons in MD years. During the MD, the number, area burned, simultaneity, and duration of large ﬁres increased signiﬁcantly compared to the control period, including the unprecedented occurrence of large ﬁres during winter. The burned area in large ﬁres increased in all vegetation types, during the MD compared to the control period, especially in the exotic plantation cover type. The regions that were most affected by ﬁre (i.e., total area burned) during the MD wereMaule, B ıo-B ıo, and Araucan ıa (35–39° S) that concentrate >75% of forest plantations in Chile. Although both maximum temperatures and precipitation are drivers of ﬁre activity, a simple attribution analysis indicates that the sustained rainfall deﬁcit during 2010–2015 was the most critical factor in the enhanced ﬁre activity. Future climate change predictions indicate more recurrent, intense, and temporally extended droughts for central and south-central Chile. Under this scenario, land-use planning and ﬁre and forest management strategies must promote a more diverse and less ﬂammable landscape mosaic limiting high load, homogenous, and continuous exotic plantations.

In January 2017, hundreds of fires in Mediterranean Chile burnt more than 5000 km2, an area nearly 14 times the 40-year mean. We contextualize these fires in terms of estimates of global fire intensity using MODIS satellite record, and provide an overview of the climatic factors and recent changes in land use that led to the active fire season and estimate the impact of fire emissions to human health. The primary fire activity in late January coincided with extreme fire weather conditions including all-time (1979–2017) daily records for the Fire Weather Index (FWI) and maximum temperature, producing some of the most energetically intense fire events on Earth in the last 15-years. Fire activity was further enabled by a warm moist growing season in 2016 that interrupted an intense drought that started in 2010. The land cover in this region had been extensively modified, with less than 20% of the original native vegetation remaining, and extensive plantations of highly flammable exotic Pinus and Eucalyptus species established since the 1970s. These plantations were disproportionally burnt (44% of the burned area) in 2017, and associated with the highest fire severities, as part of an increasing trend of fire extent in plantations over the past three decades. Smoke from the fires exposed over 9.5 million people to increased concentrations of particulate air pollution, causing an estimated 76 premature deaths and 209 additional admissions to hospital for respiratory and cardiovascular conditions. This study highlights that Mediterranean biogeographic regions with expansive Pinus and Eucalyptus plantations and associated rural depopulation are vulnerable to intense wildfires with wide ranging social, economic, and environmental impacts, which are likely to become more frequent due to longer and more extreme wildfire seasons.

http://link.springer.com/10.1007/s13280-018-1084-1

Thomson Reuters ISI

Agua y Extremos

2018

Yáñez-Morroni, G., Gironás, J., Caneo, M., Delgado, R., Garreaud, R.

Using the Weather Research and Forecasting (WRF) Model for Precipitation Forecasting in an Andean Region with Complex Topography

Atmosphere

10.3390/atmos9080304

The Weather Research and Forecasting (WRF) model has been successfully used in weather prediction, but its ability to simulate precipitation over areas with complex topography is not optimal. Consequently, WRF has problems forecasting rainfall events over Chilean mountainous terrain and foothills, where some of the main cities are located, and where intense rainfall occurs due to cutoff lows. This work analyzes an ensemble of microphysics schemes to enhance initial forecasts made by the Chilean Weather Agency in the front range of Santiago. We first tested different vertical levels resolution, land use and land surface models, as well as meteorological forcing (GFS/FNL). The final ensemble configuration considered three microphysics schemes and lead times over three rainfall events between 2015 and 2017. Cutoff low complex meteorological characteristics impede the temporal simulation of rainfall properties. With three days of lead time, WRF properly forecasts the rainiest N-hours and temperatures during the event, although more accuracy is obtained when the rainfall is caused by a meteorological frontal system. Finally, the WSM6 microphysics option had the best performance, although further analysis using other storms and locations in the area are needed to strengthen this result.

Background :Over the last decades interest has grown on how climate change impacts forest resources. However, one of the main constraints is that meteorological stations are riddled with missing climatic data. This study compared five approaches for estimating monthly precipitation records: inverse distance weighting (IDW), a modification of IDW that includes elevation differences between target and neighboring stations (IDWm), correlation coefficient weighting (CCW), multiple linear regression (MLR) and artificial neural networks (ANN). Methods: A complete series of monthly precipitation records (1995–2012) from twenty meteorological stations located in central Chile were used. Two target stations were selected and their neighboring stations, located within a radius of 25 km (3 stations) and 50 km (9 stations), were identified. Cross-validation was used for evaluating the accuracy of the estimation approaches. The performance and predictive capability of the approaches were evaluated using the ratio of the root mean square error to the standard deviation of measured data (RSR), the percent bias (PBIAS), and the Nash-Sutcliffe efficiency (NSE). For testing the main and interactive effects of the radius of influence and estimation approaches, a two-level factorial design considering the target station as the blocking factor was used. Results: ANN and MLR showed the best statistics for all the stations and radius of influence. However, these approaches were not significantly different with IDWm. Inclusion of elevation differences into IDW significantly improved IDWm estimates. In terms of precision, similar estimates were obtained when applying ANN, MLR or IDWm, and the radius of influence had a significant influence on their estimates, we conclude that estimates based on nine neighboring stations located within a radius of 50 km are needed for completing missing monthly precipitation data in regions with complex topography. Conclusions: It is concluded that approaches based on ANN, MLR and IDWm had the best performance in two sectors located in south-central Chile with a complex topography. A radius of influence of 50 km (9 neighboring stations) is recommended for completing monthly precipitation data.

Since 1981, water allocation in Chile has been based on a water use rights (WURs) market, with limited regulatory and supervisory mechanisms. The volume to be granted as permanent and eventual WURs is calculated from streamflow records, if stream gauge data are available, or from hydrologic parameter transfer from gauged to ungauged catchments, usually with less than 50 years of record. To test the per- formance of this allocation system, while analyzing the long-term natural variability in water resources, we investigated a 400 year-long (1590–2015) tree-ring reconstruction of runoff and historical water rights for Perquilauquén at Quella catchment, a tributary to the Maule River in Central Chile (35°S–36°30S). Furthermore, we assess how the current legislation would perform under a projected climate scenario, based on historical climate simulations of runoff calibrated against observed data, and future projections. Our analyses indicate that the allocation methodology currently applied by the Water Authority in Chile is very sensitive to the time window of data used, which leads to an underestimation of variability and long-term trends. According to the WURs database provided by the Chilean Water Directorate, WURs at Perquilauquén at Quella are already over-allocated. Considering regional climate projections, this condition will be exacerbated in the future. Furthermore, serious problems regarding the access and quality of infor- mation on already-granted WURs and actual water usage have been diagnosed, which further encumber environmental strategies to deal with and adapt to climate change. We emphasize the urgent need for a review and revision of current water allocation methodologies and water law in Chile, which are not concordant with the dynamics and non-stationarity of hydrological processes. Water scarcity and water governance are two of the key issues to be faced by Chile in the Anthropocene.

Anthropocene and streamflow: Long-term perspective of streamflow variability and water rights

Elementa: Science of the Anthropocene

10.1525/elementa.340

The socio-ecological sensitivity to water deficits makes Chile highly vulnerable to global change. New evidence of a multi-decadal drying trend and the impacts of a persistent drought that since 2010 has affected several regions of the country, reinforce the need for clear diagnoses of the hydro-climate changes in Chile. Based on the analysis of long-term records (50+ years) of precipitation and streamflow, we confirm a tendency toward a dryer condition in central-southern Chile (30–48°S). We describe the geographical and seasonal character of this trend, as well as the associated large-scale circulation pat- terns. When a large ensemble of climate model simulations is contrasted to observations, anthropogenic forcing appears as the leading factor of precipitation change. In addition to a drying trend driven by greenhouse gas forcing in all seasons, our results indicate that the Antarctic stratospheric ozone deple- tion has played a major role in the summer rainfall decline. Although average model results agree well with the drying trend’s seasonal character, the observed change magnitude is two to three times larger than that simulated, indicating a potential underestimation of future projections for this region. Under present-day carbon emission rates, the drying pathway in Chile will likely prevail during the next decades, although the summer signal should weaken as a result of the gradual ozone layer recovery. The trends and scenarios shown here pose substantial stress on Chilean society and its institutions, and call for urgent action regarding adaptation measures.

GIMMS NDVI time series reveal the extent, duration, and intensity of “blooming desert” events in the hyper-arid Atacama Desert, Northern Chile

International Journal of Applied Earth Observation and Geoinformation

10.1016/j.jag.2018.11.013

The “blooming desert”, or the explosive development and flowering of ephemeral herbaceous and some woody desert species during years with abnormally high accumulated rainfall, is a spectacular biological phenomenon of the hyper-arid Atacama Desert (northern Chile) attracting botanists, ecologists, geo-scientists, and the general public from all over the world. However, the number of “blooming deserts”, their geographical distribution and spatio-temporal patterns have not been quantitatively assessed to date. Here, we used NDVI data from the Global Inventory Modeling and Mapping Studies (GIMMS) project to reconstruct the annual land surface phenology (LSP) of the Atacama Desert using a non-parametric statistical approach. From the reconstructed LSP, we detected the “blooming deserts” as positive NDVI anomalies and assessed three dimensions of the events: their temporal extent, intensity of “greening” and spatial extent. We identified 13 “blooming deserts” between 1981 and 2015, of which three (1997–98, 2002–03, and 2011) can be considered major events according to these metrics. The main event occurred in 2011, spanning 180 days between July and December 2011, and spread over 11,136 km 2 of Atacama dry plains. “Blooming deserts” in Atacama have been triggered by the accumulation of precipitation during a period of 2 to 12 months before and during the events. The proposed three-dimensional approach allowed us to characterize different types of “blooming deserts”: with longer episodes or larger spatial distribution or with different “greening” intensities. Its flexibility to reconstruct different LSP and detect anomalies makes this method a useful tool to study these rare phenomena in other deserts in the world also.